Speaker placement in regards to distance apart has to do with the soundstage you would like to create and how far away from the speakers you are sitting. As a basic rule the speakers should be not further apart than you are from them. If the speakers are close together relative to your distance away the soundstage will shrink in size. If the speakers are too far apart relative to your distance away the imaging will deteriorate and the soundstage will start to break into two separate point sources of sound. So back to your question, the distance of 3 - 4 feet would be in the optimal range if you were anywhere from 3 - 8 feet away from the speakers. Above this you will start to sacrifice your soundstage size for placement but this is preferable to the other way around (placement too far apart) where you would start to lose your soundstage altogether.